This invention relates to fluid dispensing apparatus and more particularly to such an apparatus which automatically shuts off after a predetermined fluid level is achieved in the container to be filled.
Automatic dispensing nozzles of the type which automatically close when the container being filled reaches a predetermined level are known and are widely used, for example, in service stations for supplying gasoline to vehicle tanks. In these installations, the nozzles are normally arranged to be manually latched to an open position and to automatically close when the gasoline tank is substantially filled.
In one form of automatic shut-off dispensing nozzle, a venturi effect is created by the passage of the fluid through the nozzle housing which operates a diaphragm or the like for controlling an automatic trip mechanism. However, in these type of arrangements, the venturi can only produce a relatively low amount of vacuum which renders the unit relatively insensitive. This is particularly disadvantageous since in these type of mechanisms the automatic trip is usually obtained through the action of a sliding rod corporating with rolling balls or the like which selectively release same in response to the movement of the diaphragm, which is a fairly complicated arrangement requiring a relatively large amount of vacuum to cause the tripping.
Also in these type mechanisms, a mechanical packing is normally provided on the main poppet valve stem which requires a fairly large spring pressure to bias the valve to a closed position. This pressure, of course, requires a corresponding large amount of counter-pressure on the manually actuatable lever engaged by the operator, which makes the nozzle difficult to operate.